An analog-digital (A/D) conversion circuit for converting an analog input signal into a digital output signal has been used in various fields. For example, microcomputers and system LSIs include a successive-approximation type A/D conversion circuit. The successive-approximation type A/D conversion circuit samples an analog input signal and compares the analog input signal with a comparison voltage acquired from an output signal of a digital-analog converter (D/A converter). The successive-approximation type A/D conversion circuit repeats the operation from high-order bits to low-order bits of the digital output signal to determine a value of each bit of the digital output signal. Japanese Laid-Open Patent Publication No. 2010-16466 and Japanese Laid-Open Patent Publication No. 2003-283336 describe the configuration of such successive-approximation type A/D conversion circuits.
In the successive-approximation type A/D conversion circuit, each time A/D conversion of each bit is performed, a capacitor is charged or discharged by the output signal of the D/A converter. This changes the comparison voltage. Thus, the output signal of the D/A converter, which charges or discharges the capacitor, changes depending on a comparison result of a previous bit. Time required to charge or discharge the capacitor is affected by speed-up of A/D conversion. However, when a period of a charging and discharging cycle decreases due to speed-up of A/D conversion, the capacitor may not be sufficiently charged or discharged. This results in a difference between a voltage corresponding to the comparison result of the previous bit and the comparison voltage acquired through charging or discharging of the capacitor. Such a voltage difference may cause erroneous determination in the comparison operation of a next bit and decrease the accuracy of the digital output signal.